Thank you for your question to "Ask Extension".  I believe that your problem is a condition known as Bitter Pit.  Bitter pit is a physiological disorder resulting from calcium deficiency in the fruit.  There can be many reasons for low calcium.  I have provided you with a link to an article in the PNW disease management handbook that goes into detail about this condition, control methods and the cultivars that are more susceptible.
https://pnwhandbooks.org/plantdisease/host-disease/apple-malus-spp-bitter-pit
     A soil test should be conducted to confirm this issue.  I've provided you with another link to a list of Extension approved soil testing laboratories and their contact information.
https://extension.oregonstate.edu/catalog/pub/em8677
     And finally a link to an Extension publication on the proper technique on collecting a soil sample.
https://extension.oregonstate.edu/catalog/pub/ec-628-guide-collecting-soil-samples-farms-gardens
     I hope that you find this information useful, you may have to copy and paste these links into your web browser.  If this doesn't work please contact me for further assistance,  and as always Happy Gardening.